Radio hobbyist identified FBI domestic spy planes a month before mainstream news

[Zoidberg]

How I tracked FBI aerial surveillance
Those mysterious planes overhead are actually government surveillance aircraft.
_{by John Wiseman - Jun 3, 2015 7:30pm CDT}

"When mysterious aircraft began flying tight circles over Baltimore in the wake of recent protests there, it soon became clear that they were part of an FBI surveillance fleet. Here, told in his own words and tweets, is the story of how one amateur sleuth helped reveal what the feds were doing. This story was originally posted on Storify and was republished with the author's permission. John Wiseman is a Los Angeles-based engineer."

"For fun I planespot/radarspot/whatever. I have a little software defined radio dongle that I use to pick up aircraft transponder pings. I can pick up aircraft from all over the Los Angeles basin with it. I log up to one ping per second per aircraft in a database. You can see more information about the setup and information I can receive at this page: Tracking Aircraft Over Los Angeles."

[John Poet]

This appears to be the link you were trying for there
http://arstechnica.com/tech-policy/2015/06/how-i-tracked-fbi-aerial-surveillance/

[Rafman]

Some other filler info here too:
http://www.rtl-sdr.com/monitoring-fbi-surveillance-aircraft-with-ads-b-and-an-rtl-sdr/

[RCCI]

Read pretty much all of the article and link info.....What surprises me is how much I'm not surprised... I would imagine the feds have probably monitored HFU at one time or another, though with terrorist website numbers rising...the feds have bigger fish to fry..JMHO

[Fred Smith]

This is a plane that was doing much the same thing yesterday in northern Delaware. Circled for hours.